Nuclear Safety Unit: description

Bibliographie

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Safety research is closely linked to the Institute’s expert appraisal activities: it covers all of the factors (physical phenomena, equipment, measures, etc.) that contribute to the safety of nuclear facilities, with the objective of better evaluating the risks and improving the safety level of these installations. Several types of nuclear facilities exist: electricity generation reactors either in operation or being constructed such as the EPR (European pressurised reactor), experimental reactors such as the Jules Horowitz reactor currently being built on the Cadarache site, fuel reprocessing plants such as La Hague and hot laboratories, without forgetting transport of nuclear materials.

The Institute’s main areas of research into safety are focused on two major aspects reflecting the logic of defence in depth, which is the very basis of nuclear safety. The first main area of research concerns the prevention of accidents: this involves averting potential operating anomalies and system failures in order to ensure the facility keeps within its authorised range of operation. In this field, the bulk of IRSN research is grouped together into four main themes:

The ageing of components important for safety: the research being carried out aims to improve knowledge and understanding of the mechanisms of degradation of materials and equipment, as well as the means of detecting and preventing them.

New equipment technologies important for safety: the research programmes being conducted concern the means of making sure the correct behaviour of software and programmed electronic components.

The risk of criticality: the research programmes underway aim to enrich nuclear data bases and to refine the calculation methods enabling thresholds for the initiation of uncontrolled nuclear reactions to be defined.

Human and organisational factors: the research programmes concern the evaluation of risk factors that could influence human and organisational systems, especially decision making mechanisms, and targeted but nevertheless important problems such as the impact of sub-contracting.

The second main area of research concerns the limitation of the consequences of accidents: this involves better understanding the phenomenology of possible accident scenarios, including accidents involving meltdown of the reactor core, verifying the ability of safety systems to manage such accidents and – still in a logic of defence in depth – defining the measures that need to be put in place to limit their consequences and protect the public in the event of failure of these systems. The main research programmes here concern:

Protection against natural or industrial hazards: the research programmes mainly concern fires (propagation in confined environments and consequences on equipment) and earthquakes (see the environmental research unit).

The behaviour of the fuel in accidental situations: this involves acquiring a better understanding - essentially for new fuels or new fuel management methods - of the modes of degradation of the fuel during accidents involving loss of cooling or insertion of reactivity and to verify the ability of safety systems to manage such accidents.

Core meltdown accidents: the research programmes concern understanding all of the physical phenomena that could occur in the event of a core meltdown accident (corium progression, hydrogen combustion, steam explosion, corium-concrete interaction, etc.) in order, on the one hand, to conceive ways of reducing the consequences of such accidents - and also managing such accidents on new generation reactors - and, on the other hand, to evaluate possible releases of radioactivity in order to prepare the necessary measures for protecting the public and the environment.

The transfer and the confinement of radioactivity: the research programmes aim to improve understanding of the behaviour of radioactive substances, in the form of aerosols or gases, and the means of trapping them.

These programmes require important experimental and modelling resources. They are conducted to a large extent by IRSN, usually within the context of national or international partnerships. In certain fields, they rely on upstream research, carried out in collaboration with CNRS and Universities, particularly in the framework of joint research laboratories.